The polymerization of 6-aminocapronitrile to form nylon polymer is disclosed in Greenewalt U.S. Pat. No. 2,245,129, and Curatolo et al. U.S. Pat. No. 4,586,736.
When 6-aminocapronitrile is produced by partial hydrogenation of adiponitrile, hexamethylenediamine and tetrahydroazepine (THA), are coproduced. THA is represented by the formula: ##STR1##
The hexamethylenediamine is easily removed from the mixture by simple distillation, but THA is not easily separated. The presence of THA in the 6-aminocapronitrile (hereinafter sometimes referred to as 6-ACN) that is to be polymerized limits the molecular weight of the polymer and causes color and branching in the polymer. It is, therefore important that THA be removed from the 6-ACN before polymerization.
It is an object of the present invention to provide a simple and efficient method of obtaining 6-ACN that is free from THA.